1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic recording medium.
2. Description of the Related Art
Among various efforts to enhance recording density of magnetic recording media, a discrete track medium (hereinafter referred to as DTM) has been proposed in which irregularities (protrusions and recesses) are formed along a track direction on the recording surface to reduce magnetic interference between tracks and increase track density, thereby enhancing the recording density.
In some of the techniques for the discrete track medium, a pattern of protrusions and recesses is formed on a resist, and using the resist pattern by way of etching technique (mask pattern formation), isolation is achieved in the track direction in the magnetic layer. A protective layer is deposited and recesses are filled as needed.
Japanese Unexamined Patent Application Publication No. H04-310621 discloses a magnetic recording medium having a high permeability layer and a magnetic layer on a substrate, in which void areas absent of the high permeability layer and the magnetic layer are provided between tracks for recording/reproduction, to ensure the avoidance of mixing of records between the adjacent tracks on reproduction.
Japanese Unexamined Patent Application Publication No. 2006-012285 discloses a magnetic recording medium that comprises a substrate, a soft magnetic layer formed on the substrate, and a recording layer formed over the soft magnetic layer through an intermediate layer, the recording layer being divided into multiple recording elements with a predetermined pattern of protrusions and recesses.
It is asserted that cross-talk to adjacent tracks in a recording/reproduction process is eliminated and degradation of recording/reproduction performances is avoided by means of the invention of Japanese Unexamined Patent Application Publication No. 2006-012285 due to the provision of the pattern of protrusions and recesses.
The DTMs produced by way of the techniques described above are asserted to allow utilization of a commonly used raw material as a magnetic recording medium. Thus, these techniques have an advantage in possible utilization of a common magnetic recording medium.
Such a common magnetic recording medium comprises at least a magnetic layer and a protective layer formed on the magnetic layer, provided over a nonmagnetic substrate of glass or aluminum. The protective layer is generally composed a main material of carbon in view of reliability and wear resistance. A DTM is manufactured by forming a mask pattern on a magnetic recording medium (a raw medium that has a protective film on a magnetic layer over a substrate).
The manufacturing process of a DTM as described above, however, includes a step of forming a mask over the magnetic layer and forming protrusions and recesses on the magnetic layer by way of etching.
In conventional techniques, after forming protrusions and recesses on the magnetic layer, a protective film composed of a main material of carbon on the magnetic layer is removed by using oxygen plasma or a release agent containing an oxidant. As a result, degradation of magnetic performance occurs due to damage and oxidation of the magnetic recording layer by the etching process and corrosion of the magnetic recording layer by a residual component of an etching gas or etching solution. While this may be assumed not to eliminate the entire protective film, leaving a very thin film, it is extremely difficult to leave a protective film with a uniform thickness, eliminating unevenness. Therefore, the protective film needs to be completely removed.